1. Field of the Invention
The present invention relates to a radiation image information reading apparatus comprising a reading unit and an erasing unit which are combined with each other, and more particularly to a radiation image information reading apparatus of such a construction which is small in size and has a high image processing capability.
2. Prior Art
There is known a stimulable phosphor which, when exposed to radiation such as X-rays, .alpha.-rays, .beta.-rays, .gamma.-rays, cathode rays, or ultraviolet rays, stores a part of the energy of the radiation. When the phosphor exposed to the radiation is subsequently exposed to stimulating rays such as visible light, the phosphor emits light in proportion to the stored energy of the radiation.
Various proposed radiation image information recording and reproducing systems employ sheets of stimulable phosphor. In such a system, the radiation image information of an object such as a human body is recorded in a stimulable phosphor sheet, the stimulable phosphor sheet is then scanned with stimulating rays of light to emit light representing the recorded radiation image information, and then the emitted light is photoelectrically read to produce an image signal which is subsequently processed to produce a radiation image as a visible image on a recording medium such as a photographic photosensitive medium, a CRT, or the like (see Japanese Laid-Open Patent Publication Nos. 55(1980)-12429, 56(1981)-11395, 55(1980)-163472, 56(1981)-104645, and 55(1980)-116340, for example).
In the radiation image information recording and reproducing system, the stimulable phosphor sheet serves as only an image storage medium for temporarily storing radiation image information until the recorded information will be read by stimulating light rays. After the image information is read, any residual image information remaining in the sheet should preferably be erased to make the sheet reusable.
There has been proposed a radiation image information reading apparatus having a reading unit for reading image information recorded in a stimulable phosphor sheet and an erasing unit for erasing residual image information that remains in the stimulable phosphor sheet.
In the proposed radiation image information reading apparatus, a cassette containing a stimulable phosphor sheet in which radiation image information has been stored by an external recording apparatus is loaded in a cassette holder, and the stimulable phosphor sheet is taken out of the cassette and delivered to the reading unit in which the recorded image information is read from the stimulable phosphor sheet. After the image information is read, the stimulable phosphor sheet is sent to the erasing unit where any residual image information is erased from the stimulable phosphor sheet. The stimulable phosphor sheet from which the remaining image information has been erased is then removed from the radiation image information reading apparatus, and loaded into the recording apparatus for recording image information again.
There has also been proposed a radiation image information reading apparatus in which a stimulable phosphor sheet with residual image information erased therefrom is stored in a cassette again for delivery to an external recording apparatus (see Japanese Laid-Open Patent Publication No. 62(1987)-124549).
In the proposed radiation image information reading apparatus, after recorded radiation image information has been read from a stimulable phosphor sheet and any residual image information has been erased therefrom, the stimulable phosphor sheet passes through the reading unit back into the cassette. Therefore, recorded radiation image information cannot be read from a next stimulable phosphor sheet until the previous stimulable phosphor sheet is stored back in the cassette. Consequently, the proposed radiation image information reading apparatus cannot read recorded radiation image information from stimulable phosphor sheets at high speed.